Intravascular diseases are commonly treated by relatively non-invasive catheter-based techniques such as percutaneous transluminal angioplasty (PTA) and percutaneous transluminal coronary angioplasty (PTCA). Catheter-based treatment and diagnostic techniques can also include atherectomy, laser radiation, ultrasonic imaging along with others. These therapeutic techniques are well known in the art and typically involve the use of a catheter, such as a balloon catheter or catheter having some other therapeutic device located proximate a distal end of the catheter, with a guide wire, possibly in combination with other intravascular devices. A typical balloon catheter has an elongate shaft with a balloon attached proximate the distal end and a manifold attached to the proximal end. In use, a balloon catheter is advanced over a guide wire such that the balloon is positioned adjacent a restriction in a diseased vessel. The balloon is then inflated and the restriction in the vessel is opened.
A more recent technique for treating intravascular diseases includes the use of a balloon dilatation catheter to carry and place a stent within the lumen of the blood vessel at a stenosed area. The stent is a generally cylindrical body with a lumen therethrough which is balloon-expanded when placed at the site of a lesion from a compressed configuration to an expanded configuration which physically prevents the blood vessel lumen from blocking over the length of the stent. The wall of the stent is preferably made from a metallic material and includes a pattern of interconnected struts with interstitial spaces therebetween which are open through the cylindrical wall. Stents of this design are disclosed in U.S. Pat. No. 5,449,373, and in PCT publication WO 96/03092, the disclosures of which are incorporated herein by reference. Catheters specifically designed to deliver such stents are disclosed in U.S. Pat. No. 4,950,227, the disclosure of which is also incorporated herein by reference.
There are two basic types of balloon catheters used in combination with a guide wire, namely, over-the-wire (OTW) catheters and single-operator-exchange (SOE) catheters. The construction and use of both OTW catheters and SOE catheters are well-known in the art. An example of an OTW catheter may be found in commonly-assigned U.S. Pat. No. 5,047,045 to Arney et al., the disclosure of which is incorporated herein by reference. An example of an SOE balloon catheter is disclosed in commonly-assigned U.S. Pat. No. 5,156,594 to Keith, the disclosure of which is incorporated herein by reference.
PTA and PTCA catheters are preferably designed to optimize pushability, trackability and crossability. Pushability is defined as the ability to transmit force from the proximal end of the catheter to the distal end of the catheter. Trackability is defined as the ability to navigate tortuous vasculature. Crossability is defined as the ability to navigate the balloon catheter across narrow restrictions in the vasculature.
The trackability of a particular catheter design is analyzed in terms of the trackability of the distal portion of the catheter, as this portion must track the guide wire through small tortuous vessels to reach the stenosed area to be treated. A more flexible distal portion has been found to improve trackability. Further, in transitioning from a stiff proximal segment or portion of the catheter shaft to a more flexible distal portion of the catheter shaft, it has been found that kinking readily occurs at the joint between the two shaft segments of differing flexibility. The increased flexibility of the distal section also makes this portion of the catheter less able to be pushed from the proximal end of the catheter.
The crossability is related to the trackability of a particular catheter design in that crossability is affected by the flexibility of the distal section of the catheter. Further, however, the crossability of the catheter in the area of a tight lesion is effected by the design of the distal tip of the catheter. The distal tip includes that region distal of the balloon which tracks the guide wire and at the distal-most portion that portion which first must pass through a stenosed area. Thus, much effort has gone into designing tips with improved crossability such as those disclosed in co-pending application Ser. No. 08/950,864, filed on Oct. 15, 1997 and entitled "OVER-THE-WIRE CATHETER WITH IMPROVED TRACKABILITY", now U.S. Pat. No. 5,891,110, issued Apr. 6, 1999, the disclosure of which is incorporated herein by reference.
Although the above-referenced tip designs improve trackability and crossability, it has been found that these tip designs can be detrimental to the procedures utilized in placing and expanding a stent. More specifically, in the initial placement of a stent, the stent is preloaded over the deflated balloon and the improved tip designs actually help in getting the stent in place across a lesion because the tip provides a leading edge through the lesion. However, it is common procedure to then expand the stent by inflating the balloon followed by deflation of the balloon. The balloon catheter is then pulled back a distance over the guide wire and the placement of the stent evaluated under fluoroscopy. It is many times necessary to again move the balloon distally across the stent to perform a post or subsequent inflation of the balloon within the stent to properly seat the stent against the vessel wall. In these instances, the balloon catheter must be moved distally over the guide wire to position the balloon across the stent. In these situations, the tip must first pass through the interior of the stent. It has been found that tips incorporating designs which improve the crossability of the balloon catheter over a lesion can get caught on the struts of the stent when passing therethrough and make it difficult to post dilate the stent. This is particularly true in a bend where the leading edge of the tip catches the outside wall of the curve because the guide wire tends to be pressed against the outside radius of the curve while the distal-most tip of the catheter is biased that same direction as it attempts to follow the curve.
The above described problems associated with tip designs which are optimal for crossability of a lesion, but detrimental to crossing a stent are also prevalent in subsequent treatment of lesions that are distal of a stent within the same artery. To dilate a more distal lesion, the balloon dilatation catheter to be utilized must first pass through the lumen of a stent if one had been previously placed in the artery. The same problems with the tip catching on struts can occur.
Therefore, there is an unmet need for a catheter design which incorporates a tip which is designed for crossing lesions but which is also capable of being converted or modified to a second configuration which is suitable for crossing through the interior lumen of a stent without getting caught on a strut. The present invention, provides such a tip design or tip design in combination with a guide wire design which includes means for reconfiguring the distal-most portion of a catheter to prevent strut and tip interaction which is detrimental to crossing through the lumen of the stent.